Rechargeable energy storage systems are used in many different fields. One type of such implementations is electric vehicles, where a battery pack is used to provide energy to an electric motor that drives one or more wheels of the vehicle. For example, the battery pack is made of one or more cells storing the electric energy until it is used. From time to time, additional energy must be added to the energy storage system. To some extent, this can be done by regenerative braking (or “regen”), which involves converting the vehicle's kinetic energy back into electric form. Another way to replenish the electric energy level is to connect an outside power source (e.g., a DC generator) to the energy storage system. Such a power source is sometimes referred to as electric-vehicle supply equipment (EVSE).
At a general level, each EVSE operates according to the following broad steps: first, connecting equipment (e.g., a plug) is brought in physical contact with the vehicle; then, a logical handshaking process is performed to exchange the necessary information between the vehicle and the EVSE (e.g., how much energy is currently stored in the vehicle, and/or the capacity of the EVSE); finally, one or more contactors in the vehicle are closed so that there is electrical connection between the EVSE's charging conduit (sometimes called a “bus”) and the vehicle's battery system. This last step is the point when electric energy begins to flow from the EVSE into the vehicle for recharging the battery pack.
More particularly, however, each type of EVSE can operate according to any of multiple different protocols for charging of electric vehicles. One such example is the SAE J1772 standard which was established by SAE International. In particular, the protocol for DC charging under the SAE J1772 standard specifies that the bus must be energized (i.e., must be at a certain voltage level) by the time the contactors close onto the bus.
Another example of a charging protocol is CHAdeMO, which was established by a number of Japanese companies. In contrast to the SAE J1772 DC-charging protocol, CHAdeMO expects the bus to be non-energized (i.e., to be at zero volts) by the time the contactors close onto the bus. That is, the CHAdeMO EVSE does not energize the bus before the vehicle closes its contactor onto the bus.
Some electric vehicles (or other rechargeable electric equipment) operate according to another charging protocol than the examples mentioned above. For example, Tesla Motors has created a charging protocol that is not identical to any other charging protocol on the market. However, like the SAE J1772 charging protocol, the Tesla Motors charging protocol requires the bus to be at the appropriate voltage level by the time the contactors close.